EP 1 051 302 B1 describes a tire pressure adjustment apparatus of the general type under consideration. In particular, in the case of agricultural vehicles such as tractors, for example, the tire pressure can be checked and adjusted by the vehicle itself. For this purpose, in the region of the wheel connections or wheel rims, rotary transmitters allow compressed air at the tire pressure to be transmitted to the connected vehicle tires of the vehicle wheels. It is thus possible for the tire pressure to be checked and for compressed air to be replenished or discharged. The tire pressure adjustment apparatus generally has a compressed-air port for a compressed-air supply, an electronic control device, a modulator valve device actuated by way of the electronic control device, and a pressure sensor that is read out by the control device. Through corresponding actuation of the modulator valve device, a pressure transmitter can be connected, for inflation purposes, to the compressed-air supply and can be connected, for pressure measurement purposes, to the pressure sensor.
In the case of a relatively large number of wheels or axles, the number of valves required in the modulator valve device correspondingly greatly increases, which leads to considerable outlay in terms of apparatus, generally with multiple valve stages for the successive distribution of the compressed air. Correspondingly, the number of solenoid valves that must be supplied with electrical current by the control device increases.
Also, the design of the rotary transmitters for a reliable sealing-off action during tire inflation and tire pressure measurement and for reliable separation during normal operation of the vehicle generally requires a certain level of outlay in terms of circuitry. Reliable rotary transmitters are, in part, designed with a control port for the sealing-off action, that is, for pneumatic coupling, and an inflation port for inflation and pressure measurement, in order to prevent leaks and faults during inflation and pressure measurement. In the case of such a design with two ports, it is, in turn, generally possible to provide a pneumatic device—preferably in the vicinity of the axle or tire—between the modulation valve device and the rotary transmitter, and connected to the pneumatic connecting line passing from the modulation valve device. The pneumatic device initially applies a pressure shock to the control port and subsequently aerates the inflation port. Such additional pneumatic devices for the actuation of rotary transmitters are correspondingly associated with a considerable level of outlay in terms of hardware.